Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing several insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
There is a trend in the semiconductor industry towards reducing the size of features, e.g., the circuits, elements, conductive lines, vias, and contacts of semiconductor devices, in order to improve the performance of the semiconductor devices, reduce power consumption, and meet smaller packaging requirements, for example. However, as feature sizes of semiconductor devices diminish, the patterning of features becomes more challenging. The transfer of patterns of lithography masks to semiconductor devices having small feature sizes may be inaccurate or unpredictable in some applications, for example.
Double patterning is a process that is used to print small minimum feature sizes of some semiconductor devices. In double patterning, a design for conductive lines is split into two layouts. Two lithography masks are used to print alternating conductive lines, so that each mask can be imaged with better contrast due to the relaxed pitch. A patterning process flow for double patterning typically includes exposing a first resist film with a first lithography mask, transferring an image of the first mask from the first resist film into a hard mask, and stripping the first resist film. A second resist film is recoated and exposed with a second lithography mask, and the second resist image from the second lithography mask is transferred into the hard mask. The hard mask is then used as an etch mask to pattern a material layer beneath the hard mask.
However, double patterning requires two lithography masks to print a single layer, and lithography masks used for semiconductor processing are expensive. One trend is the use of multi-layer reticles (MLRs) to reduce mask costs, particularly for low volume semiconductor products. Rather than using one photo layer per lithography mask, patterns for multiple layers are placed on a single lithography mask. The exposure field is divided into subsections, and respective areas of the lithography mask are shielded off in order to expose a single layer on a semiconductor wafer. MLRs may also be used for double patterning of a single layer, for example.
However, using MLRs causes considerable additional overlay contributions, thus decreasing yields and reliability of semiconductor devices. Lithographic steppers have a distinct overlay placement signature due to lens aberrations and reticle stage distortions, for example. Likewise, when using MLRs with lithography scanners, there are similar reticle stage distortion effects.
Thus, what are needed in the art are improved lithography masks, lithography systems, and methods of manufacturing lithography masks and semiconductor devices.